---
id: CVE-2026-98983
title: 'unshare: don''t drop active namespace references that were never taken'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  unshare: don't drop active namespace references that were never taken

  Active references on the namespaces of an nsproxy are taken when the
  nsproxy is installed into a …
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= a98621a0f187a934c115dcfe79a49520ae892111 <
    56fe03a0c05dba4c5f6a23c391f96de1614a098c
  - >-
    Linux >= a98621a0f187a934c115dcfe79a49520ae892111 <
    0b6f31a3c0b16066f812e94b52a704174a6f23cd
  - Linux 27ae6b17c9ba7ff353ab0906297f08aa845782b4
  - Linux 297261b343371c4f0b31055d53d285138ec21565
  - Linux 813a47b0309097da71781ee4ac11922e39b67d55
  - Linux 6e608e3e5ce12ce7fd21e46212eccca37f917d0e
  - Linux a261fccdb4ac58ec5ba6aa1d92a6cc418fff301f
  - Linux 665dc1ed16357988d439fc5bbc860ee36f540d81
  - Linux >= 5.15.209 < 5.16
  - Linux >= 6.1.175 < 6.2
  - Linux >= 6.6.141 < 6.7
  - Linux >= 6.12.91 < 6.13
  - Linux >= 6.18.33 < 6.19
  - Linux >= 7.0.10 < 7.1
  - Linux 7.1
published: '2026-10-23'
updated: '2026-10-23'
sourceUpdated: '2026-10-23T12:20:00.918Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-98983'
references:
  - url: 'https://git.kernel.org/stable/c/56fe03a0c05dba4c5f6a23c391f96de1614a098c'
  - url: 'https://git.kernel.org/stable/c/0b6f31a3c0b16066f812e94b52a704174a6f23cd'
tags:
  - cve.org
ingestedAt: '2026-10-23T13:24:55.548Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

unshare: don't drop active namespace references that were never taken

Active references on the namespaces of an nsproxy are taken when the
nsproxy is installed into a task in switch_task_namespaces() and
copy_namespaces() and dropped again by put_nsproxy() through
deactivate_nsproxy().

But ksys_unshare() calls put_nsproxy() on an nsproxy that was never
installed when set_cred_ucounts() fails. The new namespaces of that
nsproxy go from zero to minus one and the namespaces shared with the
caller lose a reference that belongs to the nsproxy the caller keeps
using:

  WARNING: kernel/nscommon.c:171 at __ns_ref_active_put+0x1cd/0x230
   nsproxy_ns_active_put
   deactivate_nsproxy
   ksys_unshare

Afterwards the namespaces the caller lives in aren't listed by listns()
anymore. set_cred_ucounts() only fails when alloc_ucounts() can't
allocate and it only allocates when the real uid of the caller differs
from its effective uid.

Commit cefd55bd2159 ("nsproxy: fix free_nsproxy() and simplify
create_new_namespaces()") separated the two cases on purpose.
nsproxy_free() frees an nsproxy that was prepared but never installed
and that's what a failed setns() uses in put_nsset(). Export it and use
it for a failed unshare() as well.

## Affected

- `Linux >= a98621a0f187a934c115dcfe79a49520ae892111 < 56fe03a0c05dba4c5f6a23c391f96de1614a098c`
- `Linux >= a98621a0f187a934c115dcfe79a49520ae892111 < 0b6f31a3c0b16066f812e94b52a704174a6f23cd`
- `Linux 27ae6b17c9ba7ff353ab0906297f08aa845782b4`
- `Linux 297261b343371c4f0b31055d53d285138ec21565`
- `Linux 813a47b0309097da71781ee4ac11922e39b67d55`
- `Linux 6e608e3e5ce12ce7fd21e46212eccca37f917d0e`
- `Linux a261fccdb4ac58ec5ba6aa1d92a6cc418fff301f`
- `Linux 665dc1ed16357988d439fc5bbc860ee36f540d81`
- `Linux >= 5.15.209 < 5.16`
- `Linux >= 6.1.175 < 6.2`
- `Linux >= 6.6.141 < 6.7`
- `Linux >= 6.12.91 < 6.13`
- `Linux >= 6.18.33 < 6.19`
- `Linux >= 7.0.10 < 7.1`
- `Linux 7.1`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.